Sounds awesome. We're headed that way en route to World Masters in NZ this spring. Kiddos are pretty solid hikers at this point, although we'd want to back pack and overnight anything above 7 miles...anything you recommend seeing?
We've visited Oahu, Maui, and Hawaii (the Big Island) and the Big Island has definitely been my favorite. Hawaii Volcanoes National Park is a big hit. The active lava flows are constantly changing and usually require a hike to go and see. I believe there are some good camping locations within the park, but my family didn't do any camping. All of the fields of lava and craters created by volcanic activity are certainly a sight to see. Mauna Kea is really fun because you can go from sea level to almost 14,000 feet in just a couple of hours and there is often snow in the winter. They do, however, caution about kids acclimatizing that quickly. On Oahu, Diamond Head is a very popular, crowded, and short hike but still very worthwhile. The islands are quite an outdoor paradise!
How are you traveling between islands? By air? Did you have to reserve far in advance? We'll probably Space A to Hawaii out of Travis AFB, so not sure it'll be predictable. The Nat'l Park is definitely on our list, good to hear it's as awesome as we're expecting! Think we're going to take advantage of some of the military campgrounds - you know you have access to those, too, right? To say nothing of the Hale Koa...
We traveled Hawaiian Airlines between islands. I don't know anything about the reservations because my Dad took care of that...sorry. This is one of the busy times of the year so the flights seem full so I think it depends on when you are travelling. That's good to know about the campgrounds, that is something to keep in mind when I travel alone or with friends because the rest of my family isn't quite as interested in camping as I am.